The couple - who were married in September last year - have posed in bed together just as the late Beatles legend and his widow did in the presidential suite at the Amsterdam Hilton Hotel in 1969 to showcase the launch of River Island's new Come Together T-shirt in support of the international charity.
Profits from the Come Together T-shirts - which are an exact replica of that worn by John Lennon at the Cannes Film Festival in 1971 - will be donated to War Child to support its work protecting vulnerable children across the globe whose lives have been affected by the effects of war.
Millie said: ''It's an honour to be involved in this campaign. The original image is one that is moving to us all, and the work that War Child does is something that we can all be inspired by. On top of that, the T-shirt is gorgeous, so I hope everyone will get behind this and wear theirs with pride!''
Green added: ''It's great to be involved in recreating such an iconic shot with Millie. The T-shirt is in aid of a fantastic cause and carries a strong message that hopefully everyone will get behind!''
The T-shirts will be available from selected River Island stores and online from tomorrow (04.06.14), with profits from the sales going directly to War Child.
The novel's author saw a cut of the film and loved each of the changes the movie's director had made.